Image Processing Apparatus, Image Processing Method, and Non-Transitory Computer Readable Medium That Utilizes Representative Colors

1. An image processing apparatus comprising: a memory that stores instructions; a processor configured to execute the instructions to act as: an extraction unit that extracts representative colors from a target image; a color difference calculation unit that calculates a color difference between each of the representative colors and a pixel of interest of the target image; a change unit that changes a brightness component of the color difference depending on chroma of the representative colors; and a replacement unit that selects one of the representative colors depending on the color difference changed in the change unit to replace a color of the pixel of interest by the selected one of the representative colors.

2. The image processing apparatus according to claim 1 , further comprising: a classification unit that classifies the representative colors extracted in the extraction unit into a chromatic color group and an achromatic color group; and a chromatic color difference calculation unit that calculates a plurality of chromatic color differences, which are the color differences between the pixel of interest and the representative colors, and calculates one of the chromatic color differences having the smallest color difference from that of the pixel of interest, of the representative colors classified into the chromatic color group with respect to the pixel of interest, wherein when the one of the chromatic color differences is larger than a preset value, the change unit changes the brightness component of the color difference.

3. The image processing apparatus according to claim 2 , wherein the change unit further changes the brightness component of the color difference depending on chroma of the pixel of interest.

4. The image processing apparatus according to claim 2 , wherein when the one of the chromatic color differences is larger than a preset value and the chroma of the selected one of the representative colors is a preset value or less, the change unit changes the brightness component of the color difference.

5. The image processing apparatus according to claim 4 , wherein the change unit further changes the brightness component of the color difference depending on chroma of the pixel of interest.

6. The image processing apparatus according to claim 1 , further comprising: a classification unit that classifies the representative colors extracted in the extraction unit into a chromatic color group and an achromatic color group; a chromatic color difference calculation unit that calculates a plurality of chromatic color differences which are the color differences between the pixel of interest and the representative colors, and calculates one of the chromatic color differences having the smallest color difference from that of the pixel of interest, of the representative colors classified into the chromatic color group with respect to the pixel of interest; and an achromatic color difference calculation unit that calculates a plurality of achromatic color differences, which are the color differences between the pixel of interest and the representative colors, and calculates one of the achromatic color differences having the smallest color difference from that of the pixel of interest, of the representative colors classified into the achromatic color group with respect to the pixel of interest, wherein when a distance difference between the one of the chromatic color differences and the one of the achromatic color differences is a preset value or less and the difference of the brightness component between the chromatic color difference and the achromatic color difference is a preset value or less, the change unit changes the brightness component of the color difference.

7. The image processing apparatus according to claim 6 , wherein the change unit further changes the brightness component of the color difference depending on chroma of the pixel of interest.

8. The image processing apparatus according to claim 6 , wherein when the distance difference between the one of the chromatic color differences and the one of the achromatic color differences is a preset value or less, the difference of the brightness component between the chromatic color difference and the achromatic color difference is a preset value or less, and the chroma of the selected one of the representative colors is a preset value or less, the change unit changes the brightness component of the color difference.

9. The image processing apparatus according to claim 8 , wherein the change unit further changes the brightness component of the color difference depending on chroma of the pixel of interest.

10. The image processing apparatus according to claim 1 , wherein the change unit further changes the brightness component of the color difference depending on chroma of the pixel of interest.

11. A non-transitory computer readable medium storing a program causing a computer to execute the functions of the image processing apparatus according to claim 1 .

12. An image processing method comprising: extracting representative colors from a target image; calculating a color difference between each of the representative colors and a pixel of interest of the target image; changing a brightness component of the color difference depending on chroma of the representative colors; and selecting one of the representative colors depending on the changed color differences to replace a color of the pixel of interest by the selected one of the representative colors.